How can I test the function of the ignition ballast wire? I really do not need it because I switched to a Pertronix Ignitor.
According to the wiring diagram, the pink ballast wire goes from a red and green lead from the ignition switch, to the far right connector going thru the firewall. It then leaves the engine side of the connector, as red/green again, and goes to the positive side of the coil. When I check the voltage of this wire, at the coil, I always get a full 12 volts whether it is just with key on or with motor running. I've been told that you can't register the reduced voltage with a common volt meter. That does not make sense to me.
I do know that when the starter is engaged the system is supposed to deliver the full 12 volts on start up, but as I stated, it seems that I am getting it all the time. If that is the case, that's ok but I need to make sure.
Hello. 7 volts won't register as 12 volts. If the volt meter shows 12 volts, that's what you're getting.
You'd think!
Here is what I was told elsewhere. Like you, I'da thought that voltage was voltage.
"If you measure the voltage at the coil end of the wire using a high impedance volt meter with no load on the circuit you'll read full battery voltage. The resistance causes a voltage drop under load because it's limiting the current that gets to the coil. No load = no voltage drop... ."
I wanted to trace the wiring to identify the pink resistance wire. Problem is I cannot see where the 'pink' wire enters the firewall connector. Too much traffic under the dash, with the wiper motor and air conditioner. The other issue is that the wire, coming out of the loom (with the temp sender wire) to the coil, is a heavy, stiff black wire. The taped loom looks unaltered original.
So the moral is, with conflicting information, my inability to visually inspect wires and wires being a different color than the diagram specifies, I am flummoxed!!!
Last edited by Boomyal; 09-27-2009 at 09:18 PM.
Reason: spelling
Hi again. I've never heard that before, but, it would be a very simple matter to compensate for. Just start the car and check the voltage at the 'dist' or '-' post of the coil. That will be what's coming through the primary ignition circuit . I've checked the voltage at the coil more times than I could count, and gotten readings showing the reduced voltage, so, I don't know about that 'under load' thing, but, since you don't know me either, , check the voltage at the other end of the coil with the car running. That way you don't have to take anyone's word for anything.
This might help out with locating the resistor wire. The Care and Feeding of Ponies: Ignition system
..... check the voltage at the other end of the coil with the car running. That way you don't have to take anyone's word for anything. ....
Veronica, I assume by that you mean the negative side of the coil?
As far as I can tell (no other markings) that the coil is the original, orangish, yellowish topped coil. I do know that some coils have the resistance built into to them. I also assume that the OEM coil is not one of those as all the wiring diagrams show the external resistance wire.
I will do as I think you suggest and check the voltage on the negative side, with the engine running. I have already installed the Pertonix. It starts much quicker than before. But now I want to include the Pertronix flame thrower coil.
Veronica, I assume by that you mean the negative side of the coil?
Hi again. The short version of the answer is 'Yes, the negative post' . But, if someone checked the coil the same way that they would check a battery for polarity they would find that this negative post is 'power out' of the coil and the other post is 'power in'. On a battery, 'power out' is positive and 'power in' is negative. They mark the coils in a reverse polarity from batteries, generators, or any other power producing or power storing component. That's why Ford didn't mark them positive and negative. Your coil is marked 'bat' and 'dist'. Check at the post marked 'dist'.
Veronica, the night abounds in assumptions! I would take it that I should apply my meter positive to the 'dist' terminal on the coil, with the meter negative lead to ground? (while the engine is running of course)
Last edited by Boomyal; 09-28-2009 at 12:44 AM.
Reason: adddition
Veronica, the night abounds in assumptions! I would take it that I should apply my meter positive to the 'dist' terminal on the coil, with the meter negative lead to ground? (while the engine is running of course)
Hi again. I love nice, simple answers like this one. Yes, that is correct.
The DC voltage at the coil is the same all the time, there is no such thing as it changing 'under load'. If by 'load' you mean with the engine running, that makes the voltages higher because the voltage regulator will be holding the system voltage around 14V instead of the battery voltage of 12V. The only thing that makes a difference is whether the engine is running or not. If you want to make sense out of the voltages; measure then with the engine off.
With the engine off and the points OPEN there is no current to the coil. In that case you will measure battery voltage at the coil (minus a small drop for the ignition switch, etc) which, if the car has been off for several hours and you have a good battery should be 12.6 volts. If the car has run more recently you may well read a bit higher, maybe as much as 13-14 volts. With the engine off and the points CLOSED a stock coil will draw 4.5 Amp according to the shop manual. That current will drop the coil voltage down to around 6-7V.
If you try to measure it with the engine running the exact voltage you read will depend upon what meter you use (since you will be measuring a varying voltage, not a constant one), how your dwell is adjusted, how your voltage regulator is adjusted, etc. Its easier to diagnose with the engine off and there will also be less possibility of getting zapped with a spark.
These voltage measurements do not require a high impedance voltmeter. Even the worst voltmeter will have 10s of THOUSANDS of Ohms impedance. The coil and ballast resistances are in the 1-3 Ohm range and no working voltmeter will have any effect upon measuring these voltages.
If you measure battery voltage at the coil when the engine is running your ballast resistor has somehow been bypassed. With the stock coil that only makes the coil overheat with no beneficial effect(s).
The resistor wire drops the voltage available across the distributor by splitting the voltage between the resistor and the coil. If the points are open when you test the voltage you will always show battery volts because there is no load on the circuit. With the points closed you can test the voltage across the coil by putting the positive lead from your meter on the coil+ and the negative lead on the coil-. This will show you the voltage ACROSS the coil (the voltage that is available to the coil) with the points closed. You can also measure the voltage at the coil+ with the engine running but it will show a slightly higher voltage because the points are switching open to closed all the time.
I will attempt a diagram of the circuit:
______^^^^_____~~~~~~______Points___Ground
wire resistor wire coil wire points ground
You can measure the voltage ACROSS the resistor by placing the meter positive lead on the Battery+ and the meter negative lead on the coil+. This will be the voltage that the resistor is using (Vr)
Then measure the coil voltage as above. (Vc)
If you add the two (Vr + Vc) together they should be equal to battery voltage (+/- .5 Vdc)
I hope this answers the question without confusing anyone more than some of the posts here seem to. ALL voltage checks must be done with the ignition on and the points closed.(or coil- grounded)
__________________
Paul's Street and Strip Performance AODs & C4s paulstephens @ q . com 6522 51 Ave. S. Seattle, WA. 98118 206.725.0881
The DC voltage at the coil is the same all the time, there is no such thing as it changing 'under load'. If by 'load' you mean with the engine running, that makes the voltages higher because the voltage regulator will be holding the system voltage around 14V instead of the battery voltage of 12V. The only thing that makes a difference is whether the engine is running or not. If you want to make sense out of the voltages; measure then with the engine off.
Hi again. That's kind of what I started him off with. Whatever he's reading at the coil side of the resistor wire is what the coil's getting. But, apparently, someone that is a self-styled 'guru' has told him that it's different in that 'under load' situation, whatever that is.
1965 Mustang Ballast wire. 
7 volts won't register as 12 volts. If the volt meter shows 12 volts, that's what you're getting. 
, check the voltage at the other end of the coil with the car running. That way you don't have to take anyone's word for anything. 
I would take it that I should apply my meter positive to the 'dist' terminal on the coil, with the meter negative lead to ground
? (while the engine is running of course)
